100 research outputs found
Coherent control and decoherence of charge states in quantum dots
This Chapter contains a review of the recent results, both experimental and
theoretical, related to optical control of carriers confined in semiconductor
quantum dots. The physics of Rabi oscillations of exciton and biexciton
occupations, as well as time-domain interference experiments are discussed.
Next, the impact of carrier--phonon interaction in a semiconductor structure is
described and modern methods of theoretical description of the carrier--phonon
kinetics and of the resulting dephasing are presented.Comment: An introductory review chapter to appear in a book published by World
Scientifi
Two-photon coherent polarization flipping of confined excitons
A two-photon process leading to coherent transitions between the two
circularly polarized exciton states in a quantum dot is studied. It is shown
that optical flipping of the exciton polarization is possible with picosecond
laser pulses. The process is closely related to two-photon Rabi oscillations of
a biexciton but it is much more stable against shifts of the laser frequency.Comment: To be presented at the school Jaszowiec 200
Nonlinear optical response of hole-trion systems in quantum dots in tilted magnetic fields
We discuss, from a theoretical point of view, the four wave mixing
spectroscopy on an ensemble of p-doped quantum dots in a magnetic field
slightly tilted from the in-plane configuration. We describe the system
evolution in the density matrix formalism. In the limit of coherent ultrafast
optical driving, we obtain analytical formulas for the single system dynamics
and for the response of an inhomogeneously broadened ensemble. The results are
compared to the previously studied time-resolved Kerr rotation spectroscopy on
the same system. We show that the Kerr rotation and four wave mixing spectra
yield complementary information on the spin dynamics (precession and damping).Comment: 4 pages, 2 figures, conference NOEKS1
Four wave mixing spectroscopy of quantum dot molecules
We study theoretically the nonlinear four wave mixing (FWM) response of an
ensemble of coupled pairs of quantum dots (quantum dot molecules). We discuss
the shape of the FWM echo signal depending on the parameters of the ensemble:
the statistics of transition energies and the degree of size correlations
between the dots forming the molecules.Comment: Presented at the school Jaszowiec 2007. Corrected figures and some
other minor improvement
Phonon-assisted excitation transfer in quantum dot molecules
We derive a quantum-kinetic description of phonon-assisted F{\"o}rster
transfer between two coupled quantum dots (a quantum dot molecule). We show
that the exciton state decays to the ground state of the QDM via a combination
of the Rabi rotation and exponential decay. For moderately spaced dots this
process takes place on a picosecond time scale.Comment: To be presented at the school Jaszowiec 200
Phonon effects on the radiative recombination of excitons in double quantum dots
We study theoretically the radiative recombination of excitons in double
quantum dots in the presence of carrier-phonon coupling. We show that the
phonon-induced pure dephasing effects and transitions between the exciton
states strongly modify the spontaneous emission process and make it sensitive
to temperature, which may lead to non-monotonic temperature dependence of the
time-resolved luminescence. We show also that under specific resonance
conditions the biexcitonic interband polarization can be coherently transferred
to the excitonic one, leading to an extended life time of the total coherent
polarization, which is reflected in the nonlinear optical spectrum of the
system. We study the stability of this effect against phonon-induced
decoherence.Comment: 10 pages, 7 figure
Phonon-assisted tunneling between singlet states in two-electron quantum dot molecules
We study phonon-assisted electron tunneling in semiconductor quantum dot
molecules. In particular, singlet-singlet relaxation in a two-electron doped
structure is considered. The influence of Coulomb interaction is discussed via
comparison with a single electron system. We find that the relaxation rate
reaches similar values in the two cases but the Coulomb interaction shifts the
maximum rates towards larger separations between the dots. The difference in
electron-phonon interaction between deformation potential and piezoelectric
coupling is investigated. We show that the phonon-induced tunneling between
two-electron singlet states is a fast process, taking place on the time scales
of the order of a few tens of picoseconds.Comment: Final extended version, 8 pages, 9 figure
Accuracy of effective mass equation for a single and double cylindrical quantum dot
In this contribution we study the accuracy of various forms of electron
effective mass equation in reproducing spectral and spin-related features of
quantum dot systems. We compare the results of the standard 8 band k.p model to
those obtained from effective mass equations obtained by perturbative
elimination procedures in various approximations for a cylindrical quantum dot
or a system of two such dots. We calculate the splitting of electronic shells,
the electron g-factor and spin-orbit induced spin mixing and show that for a
cylindrical dot the g-factor is reproduced very exactly, while for the two
other quantities the effective mass equation is much less accurate
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